It is well known, particularly in the field of transporting and using particulate materials, commonly coarse powders, granules, pellets, and the like that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, and streamers (ribbon-like elements that can “grow” into quite long and tangled wads that will impede the flow of materials or even totally block the flow). The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants.
The term “contaminant” as used herein includes a broad range of foreign material, as well as the broken particles, dust, fluff and streamers mentioned in the preceding paragraph. In any case, contaminants are detrimental to the production of a high quality product, and in some situations a health risk to employees of the producer and possibly even a source of danger in that some contaminants can produce a dust cloud which, if exposed to an ignition source, may explode.
Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and, therefore, cannot be sold. Heat in the injection molding machine can vaporize dust that leads to tiny gas bubbles in the finished product. Heat also burns dust and causes “black spots”, actually carbonized dust. Sometimes dust pockets in the machine don't melt and cause “soft spots” or “white spots” as these defects are commonly called. It is important to note that, since these same non-uniform materials often do not melt at the same temperature as the primary product, the un-melted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and, thus, increased overall production costs.
Conventional particulate material dedusting devices, such as is disclosed in U.S. Pat. No. 5,035,331, granted to Jerome I. Paulson on Jul. 30, 1991, utilize first and second wash decks, formed as sloped planar surfaces within the apparatus and having openings therein for the passage of pressurized air therethrough to pass through particulate material flowing along the wash decks. Between the two wash decks, the particulate material passes through a Venturi zone, which combined with the passage of air through the particulate material on the wash decks, discharges dust and other contaminates upwardly with the air flow to be discharged from the apparatus.
In U.S. Pat. No. 7,380,670, granted on Jun. 3, 2008, to Jerome I. Paulson, Heinz Schneider and Paul Wagner, a compact dedusting apparatus having back-to-back wash deck assemblies, provides increased capacity by doubling the wash decks and the Venturi zones, which requires the inflow of particulate material to be equally divided between the two wash deck assemblies. In both U.S. Pat. No. 5,035,331 and U.S. Pat. No. 7,380,670, a magnetic flux field is applied to the infeed of particulate material to neutralize the static charges attracting the contaminates to the particulate pellets to enhance the operation of the wash decks in separating contaminates from the particulate material.
Accordingly, it would be desirable to provide a dedusting apparatus that would be operable to clean contaminates from greater quantities of particulate material without increasing the overall size of the dedusting apparatus, while providing wash deck and Venturi zone operations similar to that of conventional planar wash deck dedusting apparatus.